In order to improve properties of medical flexible plastic containers such as bag for infusion fluid, trials of employing a multilayered film as a material have been made. Examples of a conventional multilayered container include those made of a polyethylene resin described below.
1) Japanese Laid-Open Patent Publication No. 62-64363
A three-layer bag made of a linear low-density polyethylene, wherein the density of inner/outer layers is not less than 0.920 g/cm3 and that of an intermediate layer is smaller than 0.920 g/cm3.
2) Japanese Laid-Open Patent Publication No. 63-248633
A three-layer container made of a linear low-density polyethylene, wherein the density of inner/outer layers is from 0.910 to 0.940 g/cm3 and that of an intermediate layer is from 0.880 to 0.905 g/cm3 and, furthermore, a difference in density between the both layers is not less than 0.01 g/cm3. 
3) Japanese Laid-Open Patent Publication No. 3-277365
A three-layer bag wherein an outer layer is made of a linear low-density polyethylene having a density of not less than 0.920 g/cm3 and an intermediate layer is made of a linear low-density polyethylene having a density of not more than 0.915 g/cm3 and, furthermore, an inner layer is made of a branched low-density polyethylene having a density of not less than 0.918 g/cm3.
4) Japanese Laid-Open Patent Publication No. 4-266759
A three or more-layer bag wherein an outer/inner layer is made of a resin prepared by mixing a linear branched low-density polyethylene having a density of not more than 0.930 g/cm3 with 5 to 40% of a high-density polyethylene having a density of not less than 0.945 g/cm 3 and an intermediate layer is made of a resin prepared by mixing a linear low-density polyethylene having a density of not more than 0.920 g/cm3 with 15% or less of the above-described high-density polyethylene.
However, the above-described conventional medical multilayered containers have some of the following drawbacks.
(i) Since the inner/outer layers of the film are composed of a polyethylene resin having a low-density, the heat resistance is not sufficient and seal and drop strengths are lowered by sterilization under high-temperature conditions, such as steam sterilization under high pressure, hot-water sterilization or the like.
(ii) After the completion of the sterilization under high-temperature condition, blocking is liable to be caused (low blocking resistance).
(iii) The wall thickness must be increased because of low strength of the film.
(iv) The rate of producing the bag can not be increased because of insufficient tensile strength of the film.
(v) Since the temperature of a heater can not be increased on heat sealing, sealing can not be conducted in a short time (low sealability).
(vi) The transparency and flexibility of the film are lowered after the completion of the sterilization.
In case a medical container (bag for infusion fluid) 10 shown in FIG. 1 is produced, two films 22 are laid one upon another and then the periphery of the film 22 is heat-sealed in the state where a port member (port) 20 is interposed between two films 22.
However, as shown in FIG. 2, the film 22 bends largely at the portion adjacent to the port member 20. Therefore, when a conventional multilayered film is heat-sealed, the film is stretched at the bend portion 24, and film thickness is reduced, so pinholes are likely to occur.
Therefore, an object of the present invention is to provide a multilayered film which is superior in heat resistance, blocking resistance, strength, sealability, transparency and flexibility, and which is capable of preventing pinholes from occurring at the bend portion on heat sealing.